Error "NullReferenceException" Help Please

I have a server dedicated to 7 days to die on the 4netplayers page. A friend after playing many hours, a console error appears when loading the server that says: "NULLREFERENCEEXCEPTION: Object reference not set to an instance of an objetc". only that person happens to the rest of the users of the server we access without problem. Can you help me solve my friend's problem. Thank you so much.